So, I'm reading...an early 2007 Wizard magazine (so I'm behind, sue me!)...and it features Penance as someone who emerged from the Stamford massacre and keys off pain...

Isn't this Speedball?

Yes. One of the main stories in Civil War: Frontline is Robbie's transition from Speedball into Penance. It isn't public knowledge that the two are one in the same, but everyone on the Thunderbolts team, as well as several other superheroes, knows about it.

How'd Speedball have his power change from kinetic to pain?

When he was caught in the explosion in Stamford his kinetic powers protected him, sending him across two states (or something like that). Two guys found him in a field, unconscious, with his kinetic powers holding him aloft. When they got close to him, the kinetic energy exploded and killed both of them. After that, it looked like his powers were completely gone. He was sent to prison, and was shived in a prison fight, which caused his new powers to go off and knock everyone out, but he couldn't figure out how to activate it again. The entire time, he was trying to plead his case and get to court so he could make his argument that he and the New Warriors weren't responsible for the explosion in Stamford. When he finally gets his chance, a parent of one of the children who died shoots him. On the way to the hospital, his powers explode again, killing the paramedics and wounding his lawyer, She-Hulk. This is when he figures out that pain is what is triggering his new powers to go off. The doctors saved his life, but they couldn't get all of the bullet fragments out of his spine. Robbie agrees to register, but burns his Speedball costume. Because pain activates his powers, he has a costume designed with spikes all over the inside, one for every person that was killed in Stamford and as a result of his later actions.

As I understand, this was all psychological, as after talking with Doc Samson in the most recent Thunderbolts story, he was able to use his Speedball powers again. He was letting pain activate his powers as his way of making "penance" for the deaths he caused.